BeginnerTopic 8 of 112Civil & Structural
Aggregates
Sand and gravel provide bulk and strength in concrete.
In depth
Aggregates (60–75% of concrete volume) include sand (fine, <4.75 mm) and gravel or crushed stone (coarse). Requirements: strength, grading, cleanliness, shape and low reactivity. Good grading reduces voids and cement need. Moisture content affects the mix.
Key points
- Sieve analysis and fineness modulus
- Alkali-silica reaction
- Recycled aggregates
ExampleRounded river gravel gives better workability than angular crushed rock.
Aggregates make up most of the volume of concrete, so their grading and quality strongly affect strength, workability and shrinkage.
What is Aggregates?
Sand and gravel provide bulk and strength in concrete.
Why is it important to understand aggregates?
Aggregates make up most of the volume of concrete, so their grading and quality strongly affect strength, workability and shrinkage.
Why does the grading of aggregates matter?
A well-graded mix has fewer voids, so less cement paste is needed for good packing and strength.
What is a common problem with poor aggregates?
Dirty or weak particles reduce strength, and reactive aggregates can cause long-term expansion and cracking.
How is Aggregates used in practice?
Typical applications include checking that sand is well graded for a pumped concrete mix, rejecting a gravel with high clay content for a structural pour and choosing a lightweight aggregate for a floor on a weak structure.
What should I learn before Aggregates?
Study "Cement and its types" first (topic 7 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Aggregates?
Sieve analysis and fineness modulus. Alkali-silica reaction. Recycled aggregates.
Can you give an example of Aggregates?
Rounded river gravel gives better workability than angular crushed rock.
What comes after Aggregates?
The next topic is "Concrete mix design", which builds directly on this one.
How difficult is Aggregates?
It is classed as Beginner in Civil & Structural (topic 8 of 112). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.